User operated drug delivery devices are as such known in the prior art. They are typically applicable in circumstances, in which persons without formal medical training, i.e., patients, need to administer an accurate and predefined dose of a medicament, such as heparin or insulin. In particular, such devices have application, where a medicament is administered on a regular or irregular basis over a short-term or long-term period.
In order to accommodate with these demands, such devices have to fulfil a number of requirements. First of all, the device must be robust in construction, yet easy to use in terms of handling and in understanding by the user of its operation and the delivery of the required dose or medicament. The dose setting must be easy and unambiguous. Where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose.
Drug delivery devices, in particular injection devices, such like pen-type injectors are designed and adapted for self-medication, where a user or patient, e.g. suffering a chronic disease regularly utilises the drug delivery device. With such injection devices, a disposable injection needle is for instance to be removably attached to a distal dispensing end of the device. At least for injecting of a dose of the medicament, the free and tipped end of an injection needle may be at least temporally exposed to the environment or to the user. An exposed needle always represents a certain danger to health. The patient himself or other persons may be therefore exposed to an increased risk of a needle stitch.
There already exist safety shield systems for such pen needles as for instance described in US 2008/0177238 A1. There, the safety shield system is integrated in a disposable needle assembly, which after a single use is to be discarded due to hygienic reasons. Since the safety shield system is rather elaborate such safety needle assemblies are comparatively expensive compared to non-shielded disposable needle assemblies conventionally to be used with pen-type injectors.
It is therefore an object of the present invention to provide a drug delivery device with an improved protection mechanism to avoid inadvertent needle stitches. It is a particular aim of the present invention to provide a protection mechanism for an injection device, which allows to make use of conventional disposable injection needles, especially with pen-type injectors. Moreover, the protection mechanism should be particularly applicable to all-mechanically implemented drug delivery devices exclusively operated and driven by a manual handling of a user. The protection mechanism is particularly adapted for repeated use with a series of injection needles.